1. Field of the Invention
The present disclosure relates to the device and the method for printing an alignment film. Particularly, the present disclosure relates to the printing plate and the method for printing an alignment film thereof.
2. Discussion of the Related Art
The active matrix type liquid crystal display device (or “LCD device”) represents video data using a thin film transistor (or “TFT”) as a switching element. The liquid crystal display device is smaller than the cathode ray tube (or “CRT”) so that is is easily applied as the display device for portable information device, office automation device, computer and so on. Furthermore, it is rapidly applied as the television display replacing the CRT.
FIG. 1 illustrates some portions of the pixel array in the active matrix liquid crystal display device.
Referring to FIG. 1, on the lower glass substrate of the liquid crystal display device (GLSL) a TFT array is formed, and on the upper glass substrate of the LCD device (GLSU) a color filter array is formed. The TFT array on the lower glass substrate (GLSL) includes the data lines (DL) and the gate lines (GL) crosswisely disposed each other, and the TFTs formed at each crossed portions of the data lines and gate lines, and the pixel electrodes connected to each TFTs. The color filter array of the upper glass substrate (GLSU) includes a black matrix (BM), a color filter (CF) and a common electrode (COM).
On the light incident surface of the lower glass substrate (GLSL), a lower polarization plate is attached, and on the light outgoing surface of the upper glass substrate (GLSU) a upper polarization plate is attached. The light absorbing axis of the lower polarization plate and the upper polarization plate are perpendicularly crossed. In addition, alignment films are formed on the inner surfaces of the lower glass substrate (GLSL) and the upper glass substrate (GLSU) with which the liquid crystal layer (LC) is contacted.
As it is difficult to get a desired aligning condition of the liquid crystal material molecules just by injecting the liquid crystal material between the glass substrates, the alignment films should be formed in the LCD device to set pre-tilt angle of the liquid crystal molecules.
As shown in FIG. 2, the device for printing an alignment film includes a printing roller 21 around which printing plate (RPL) is rolled, an anilox roller 22, a doctor blade 24, a dispenser 25, and a doctor roller 26.
The printing roller 21 contacts the anilox roller 22 so that it is supplied with alignment film material 23 from the anilox roller 22. For the alignment film material 23, generally a polyimide is selected. At one side of the printing roller 21, a pinion gear is engaged and a rack gear is engaged with the pinion gear. The printing roller 21 interlocks with the pinion gear and the rack gear so that it rolls and moves linearly along the arrow line direction and then it transcribes the alignment film material 23 coated on the printing plate (RPL) to the glass substrate 20 of the LCD device. While the printing roller 21 transcribes the alignment film material on the glass substrate 20 of the LCD device, the glass substrate 20 is attached to the stage by a vacuum force.
The alignment film material 23 is supplied to the anilox roller 22. By rotating the anilox roller 22 and the printing roller 21 in opposite directions to each other, the alignment film material 23 coated on the anilox roller 22 is transcribed to the printing roller 21.
The doctor blade 24 shaves off the alignment film material 23 supplied to the anliox roller 22 by the dispenser 25. In order to make uniformly the thickness of the alignment film material coated on the anilox roller 22, the alignment film printing device shown in FIG. 2, includes the doctor roller 26. The doctor roller 26, as disposed as close to the anilox roller 22, presses the alignment film material 23 coated on the anilox roller 22, and rotates to opposite direction to the anilox roller 22 to make the thickness of the alignment film material 23 uniform.
Due to the dummy relief (or embossing) pattern of the printing plate (RPL) rolled around the printing roller 21, when the printing roller 21 and the anilox roller 22 are rotating, periodically an impact force is applied to the anilox roller 22. The impact force may cause a gap between the anilox roller 22 and doctor blade 24 and vary the pressing amount of the doctor roller 26 to the anilox roller 22. Therefore, the thickness of the alignment film material coated on the printed plate (RPL) may be varied (not uniform). In this case, the alignment of the liquid crystal molecules becomes irregular and the cell gap becomes uneven. This causes a defect on the display panel.
In more detail, every time when the impact force due to the level difference of dummy relief (embossing) pattern formed on the printing plate (RPL) is applied to the anilox roller 22, the pressing force of the doctor roller 26 to the anilox roller 22 is excessively increased. As a result, the doctor roller 26 does not rotate while being contacted to the anilox roller 22 but is dragged on the anilox roller 22. As shown in FIG. 3, the dragging trace 31a of the doctor roller 26 formed on the alignment film material 23 coated on the anilox roller 22 is also transcribed to the printing plate (RPL) rotating by interlocking with the anilox roller 22. The dragging trace 31b of the doctor roller 26 transcribed on the printing plate (RPL) is also transcribed to the glass substrate of the LCD device. Therefore, the alignment film has the unwanted dragging trace so that a strain in horizontal direction may be shown when the display is operating.
FIG. 4 illustrates one embodiment of the printing plate applied to the method of obtaining a multi-panel by cutting a single glass.
Referring to FIG. 4, the printing plate (RPL) includes a base film (SUBS) and a first and a second resin plates (RUB1 and RUB2) formed on the base film (SUBS). The base film (SUBS) is made of PET (“poly ethylene terephthalate”). The first and the second resin plates (RUB1 and RUB2) are parallelly attached on the base film (SUBS) a predetermined distance apart from each other. Furthermore, the sides of the resin plate (RUB1 and RUB2) facing each other are adhered by adhesives (BO).
On each of resin plates (RUB1 and RUB2), embossing patterns (or “ED”) PA1 to PA6, and grooved patterns (GR) are formed. The embossing patterns include a dummy embossing pattern (ED) formed in closed loop shape along with 4 edges and pixel array embossing patterns PA1 to PA6 corresponding to the pixel array of the LCD device. To the embossing patterns, the alignment film material 23 is transcribed from the anilox roller 22. The grooved patterns is formed between the neighboring embossing patterns PA1 and PA6, and between the pixel array embossing pattern PA1 to PA6 and the dummy embossing pattern (ED) with having a predetermined depth (t1). The depth (t1) of the grooved patterns (GR) is less than the printing plate (RPL) thickness (tt).
In the method of obtaining a multi-panel by cutting a single glass, a plurality of pixel arrays (LCDPA1 to LCDPA6) are on one large mother glass substrate (GLSM) as shown in FIG. 5. In FIG. 4, the pixel array embossing patterns (PA1 to PA6) formed on the resin plates (RUB1 and RUB2) transcribe the alignment film material to the pixel arrays (LCDPA1 to LCDPA6) formed on the large mother glass substrate (GLSM) of LCD device shown in FIG. 5. The pixel arrays of the mother glass substrate (GLSM) include TFT array or color filter array.
In the printing plate (RPL) of the FIG. 4, the dummy embossing patterns (ED) and the pixel array embossing patterns (PA1 to PA6) are overlayed along with the forwarding direction or rotating direction (x) of the printing roller 21 against the glass substrate 20 of the LCD device so that the strain such as the dragging trace of the doctor roller 26 due to the dummy embossing pattern (ED) is also transcribed to the alignment film material on the pixel array embossing patterns (PA1 to PA6). In the interim, when an impact force is applied to the anilox roller 22 due to the level difference between the upper surface of the resin plates (RUB1 and RUB2) and the upper surface of the adhesive (BO), the pressing force of the doctor roller 26 to the anilox roller 22 is varied and the gap between the anilox roller 22 and the doctor blade 24 is uneven so that the strain may be transcribed to the alignment film material on the printing plate (RPL). The strain transcribed to the alignment film material on the anilox roller 22 is still remained at the next rotation, so that the strain may be transcribed to the pixel array embossing patterns (PA1 to PA6) of the printing plate (RPL) periodically in certain time interval.